The present invention relates to a process for producing anhydrous alkali sulfide.
In the dry state and when finely dispersed, alkali sulfides can react with air at elevated temperature, giving rise to considerable potential risk and product losses during thermal drying. This represents a major processing and safety obstacle to the performance of such a process.
The production of anhydrous alkali sulfide by vacuum contact drying, starting from the solid containing water of crystallization, is known from EP 0 924 165 A1.
Furthermore, the convective spray drying of anhydrous alkali sulfides using hot, anhydrous inert gases, is known from WO 01/25146.
The disadvantage of the known processes using anhydrous inert gases, such as e.g. nitrogen, as the drying gas in a pass-through operation lies in the high operating costs. Gas recycling is therefore desirable. However, recycled gas may no longer be entirely anhydrous and therefore has to be dried.
An object of the present invention is to provide a process wherein a gas recycling operation is possible without drying the gas.